From 111cf65e92cc2ea982601b7df2ed7af6ac1565dc Mon Sep 17 00:00:00 2001 From: Nathaniel Beaver Date: Fri, 11 Sep 2015 12:28:39 -0500 Subject: [PATCH] Move discussion of external volumes to architectural considerations. --- README.rst | 272 ++++++++++++++++++++++++++--------------------------- 1 file changed, 136 insertions(+), 136 deletions(-) diff --git a/README.rst b/README.rst index ba2af2e..5ad4651 100644 --- a/README.rst +++ b/README.rst @@ -516,142 +516,6 @@ For example, the Linux port of the `Unity engine`_ has `issues with case-sensiti https://archive.org/stream/Intro_to_CPM_Feat_and_Facilities/Intro_to_CPM_Feat_and_Facilities_djvu.txt ------------------------------------------ -Limitations on access to external volumes ------------------------------------------ - -When accessing external volumes such as flash drives, -Windows assigns different capital letters to each volume -each corresponding to a different absolute path root. -This is necessary for backwards compatibility with MS-DOS, -but it is not without drawbacks. - -Perhaps the most obvious problem -is that there are only 26 letters in the English alphabet. -But what does this mean in practice? - -For example, the drive letter may be different when a drive is reconnected, -but applications that track recently used files -will look for files under the old drive letter, -and be unable to find the files. - - I have a problem with Word when working with documents on my flash drive. - If I insert the drive days later and try to use the recently used file - list, Word sometimes says it can’t find the document. - - I’ve worked out that when I insert the flash drive it’s not always using - the same drive letter – it’s F or G drive but occasionally even later in - the alphabet. - - How can I change the flash drive letter or, even better, make it appear as - the same drive letter each time? - -http://new.office-watch.com/2008/make-a-consistent-drive-letter-or-path-to-a-removable-drive/ - -Both of these problems can be solved using NTFS mount points, -but Windows doesn't use them by default. -There are also other limitations; -for example, the recycle bin doesn't work as expected. - - The problem is the recycle bin. This "undo" option is maintained with a hidden - system file that is on the partition that holds the files being deleted. - Unfortuantely, when the command to delete a folder is given, the system - attempts to delete the folder using the mount point folder's Master File Table, - and not the subfolder's Master File Table. The mount point folder's MFT - doesn't host the record, and an access denied message is kicked back to you for - having the temerity to try and recycle a directory which apparently doesn't - even exist! The only solution for this is to not recycle subfolders and - directories, but to outright delete them. - -http://getyouriton.blogspot.com/2009/08/serious-gotchas-with-mounted-drives-or.html - -This is related to an inconsistency -of the Windows operating system: -the NTFS filesystem has a root directory, -but Windows itself has no unique root directory. - -(*My Computer* roughly corresponds to a root directory in concept, -and looks like a folder when viewed in Windows Explorer, -but there is no actual *My Computer* folder anywhere on the filesystem.) - -Unix, on the other hand, -has a unique root directory -and mounts drives (including removable media)_ -as directories on the filesystem. [#disk_location]_ - -On Linux, flash drives are mounted under ``/media/``, -are assigned a directory based on their label, -and the assigned directory won't change unless the partition label changes -or the drive is manually mounted somewhere else. -For graphical file managers, -each flash drive has its own trash folders, -one per user. - -https://superuser.com/questions/169980/what-is-trash-and-trash-1000 - -https://unix.stackexchange.com/questions/93960/why-is-linuxs-filesystem-designed-as-a-single-directory-tree - -.. http://www.tmsbackup.com/cms/index.php?id=652 -.. http://www.techrepublic.com/blog/the-enterprise-cloud/use-mount-points-if-you-run-out-of-windows-drive-letters/ -.. https://stackoverflow.com/questions/4652545/windows-what-happens-if-i-finish-drive-letters-they-are-26 -.. https://technet.microsoft.com/en-us/library/cc938934.aspx -.. https://serverfault.com/questions/83165/mount-drive-with-two-drive-letters-instead-of-one -.. https://support.microsoft.com/en-us/kb/307889 - -http://www.zdnet.com/article/dear-microsoft-its-time-to-stop-using-drive-letters-and-whacks/ - -.. https://support.microsoft.com/en-us/kb/947021 - - Volume mount points are robust against system changes that occur when devices - are added or removed from a computer. - -https://technet.microsoft.com/en-us/library/Cc938934.aspx - -.. [#disk_location] - - Multics, the predecessor to Unix, - appears to be the first operating system with a root directory - and a hierarchical filesystem underneath it. - - .. TODO: source - - However, the motivations for such a scheme go back further. - One of the most influential time-sharing systems, - CTSS, recognized the need for accessing files independent of their disk location. - - All files kept on the disk (and drum) are known to the - user only by name: the supervisor disk control module keeps - for each user a directory of names and corresponding track - locations on the disk. - - https://archive.org/stream/bitsavers_mitctssMAC5_3662592/MAC-TR-16_CTSStecNote_Mar65_djvu.txt - - It is desirable, from the point of view both of programming and - of disk administration, that the user have no notion of the absolute - location where his files of information are stored in the disk. Rather, - the user will refer to his files only by symbolic names and logical mode - number. - - https://archive.org/stream/bitsavers_mitctssCTS_3840198/CTSS_ProgrammersGuide_djvu.txt - - Unix was developed on relatively small disk drives, - so it was useful to be able mount drives anywhere on the filesystem. - - You know how Ken Thompson and Dennis Ritchie created Unix on a PDP-7 in 1969? - Well around 1971 they upgraded to a PDP-11 with a pair of RK05 disk packs (1.5 - megabytes each) for storage. - - When the operating system grew too big to fit on the first RK05 disk pack (their - root filesystem) they let it leak into the second one, which is where all the - user home directories lived (which is why the mount was called /usr). They - replicated all the OS directories under there (/bin, /sbin, /lib, /tmp...) and - wrote files to those new directories because their original disk was out of - space. When they got a third disk, they mounted it on /home and relocated all - the user directories to there so the OS could consume all the space on both - disks and grow to THREE WHOLE MEGABYTES (ooooh!). - - http://lists.busybox.net/pipermail/busybox/2010-December/074114.html - --------------------- Filename restrictions @@ -896,6 +760,142 @@ These are limitations of the Windows platform which are not intrinsic to the operationg system, but nevertheless cause problems. +----------------------------------------- +Limitations on access to external volumes +----------------------------------------- + +When accessing external volumes such as flash drives, +Windows assigns different capital letters to each volume +each corresponding to a different absolute path root. +This is necessary for backwards compatibility with MS-DOS, +but it is not without drawbacks. + +Perhaps the most obvious problem +is that there are only 26 letters in the English alphabet. +But what does this mean in practice? + +For example, the drive letter may be different when a drive is reconnected, +but applications that track recently used files +will look for files under the old drive letter, +and be unable to find the files. + + I have a problem with Word when working with documents on my flash drive. + If I insert the drive days later and try to use the recently used file + list, Word sometimes says it can’t find the document. + + I’ve worked out that when I insert the flash drive it’s not always using + the same drive letter – it’s F or G drive but occasionally even later in + the alphabet. + + How can I change the flash drive letter or, even better, make it appear as + the same drive letter each time? + +http://new.office-watch.com/2008/make-a-consistent-drive-letter-or-path-to-a-removable-drive/ + +Both of these problems can be solved using NTFS mount points, +but Windows doesn't use them by default. +There are also other limitations; +for example, the recycle bin doesn't work as expected. + + The problem is the recycle bin. This "undo" option is maintained with a hidden + system file that is on the partition that holds the files being deleted. + Unfortuantely, when the command to delete a folder is given, the system + attempts to delete the folder using the mount point folder's Master File Table, + and not the subfolder's Master File Table. The mount point folder's MFT + doesn't host the record, and an access denied message is kicked back to you for + having the temerity to try and recycle a directory which apparently doesn't + even exist! The only solution for this is to not recycle subfolders and + directories, but to outright delete them. + +http://getyouriton.blogspot.com/2009/08/serious-gotchas-with-mounted-drives-or.html + +This is related to an inconsistency +of the Windows operating system: +the NTFS filesystem has a root directory, +but Windows itself has no unique root directory. + +(*My Computer* roughly corresponds to a root directory in concept, +and looks like a folder when viewed in Windows Explorer, +but there is no actual *My Computer* folder anywhere on the filesystem.) + +Unix, on the other hand, +has a unique root directory +and mounts drives (including removable media)_ +as directories on the filesystem. [#disk_location]_ + +On Linux, flash drives are mounted under ``/media/``, +are assigned a directory based on their label, +and the assigned directory won't change unless the partition label changes +or the drive is manually mounted somewhere else. +For graphical file managers, +each flash drive has its own trash folders, +one per user. + +https://superuser.com/questions/169980/what-is-trash-and-trash-1000 + +https://unix.stackexchange.com/questions/93960/why-is-linuxs-filesystem-designed-as-a-single-directory-tree + +.. http://www.tmsbackup.com/cms/index.php?id=652 +.. http://www.techrepublic.com/blog/the-enterprise-cloud/use-mount-points-if-you-run-out-of-windows-drive-letters/ +.. https://stackoverflow.com/questions/4652545/windows-what-happens-if-i-finish-drive-letters-they-are-26 +.. https://technet.microsoft.com/en-us/library/cc938934.aspx +.. https://serverfault.com/questions/83165/mount-drive-with-two-drive-letters-instead-of-one +.. https://support.microsoft.com/en-us/kb/307889 + +http://www.zdnet.com/article/dear-microsoft-its-time-to-stop-using-drive-letters-and-whacks/ + +.. https://support.microsoft.com/en-us/kb/947021 + + Volume mount points are robust against system changes that occur when devices + are added or removed from a computer. + +https://technet.microsoft.com/en-us/library/Cc938934.aspx + +.. [#disk_location] + + Multics, the predecessor to Unix, + appears to be the first operating system with a root directory + and a hierarchical filesystem underneath it. + + .. TODO: source + + However, the motivations for such a scheme go back further. + One of the most influential time-sharing systems, + CTSS, recognized the need for accessing files independent of their disk location. + + All files kept on the disk (and drum) are known to the + user only by name: the supervisor disk control module keeps + for each user a directory of names and corresponding track + locations on the disk. + + https://archive.org/stream/bitsavers_mitctssMAC5_3662592/MAC-TR-16_CTSStecNote_Mar65_djvu.txt + + It is desirable, from the point of view both of programming and + of disk administration, that the user have no notion of the absolute + location where his files of information are stored in the disk. Rather, + the user will refer to his files only by symbolic names and logical mode + number. + + https://archive.org/stream/bitsavers_mitctssCTS_3840198/CTSS_ProgrammersGuide_djvu.txt + + Unix was developed on relatively small disk drives, + so it was useful to be able mount drives anywhere on the filesystem. + + You know how Ken Thompson and Dennis Ritchie created Unix on a PDP-7 in 1969? + Well around 1971 they upgraded to a PDP-11 with a pair of RK05 disk packs (1.5 + megabytes each) for storage. + + When the operating system grew too big to fit on the first RK05 disk pack (their + root filesystem) they let it leak into the second one, which is where all the + user home directories lived (which is why the mount was called /usr). They + replicated all the OS directories under there (/bin, /sbin, /lib, /tmp...) and + wrote files to those new directories because their original disk was out of + space. When they got a third disk, they mounted it on /home and relocated all + the user directories to there so the OS could consume all the space on both + disks and grow to THREE WHOLE MEGABYTES (ooooh!). + + http://lists.busybox.net/pipermail/busybox/2010-December/074114.html + -------------------------------- Limited default debugging tools. --------------------------------